[ODE] Problem interfacing ODE to my motor-control library

[Remi.Coulom]

Hello,

As I wrote in a previous post, I am trying to connect my motor-control 
library to ODE. The problem I have is that I need a deeper access to the 
simulation than what is provided by the stepping functions of the API. 
According to what I have understood, I'll have to understand the 
internals of ODE. Before I try to do that, I thought it might be a good 
idea to ask the list for advice first, because I have no idea how 
difficult it would be, or whether it is possible at all.

This is what I need: My library deals with systems where the dynamics 
are linear with respect to control variables. That is to say, if the 
state is described by vector x (positions, angles, velocities), and 
control variables are vector u (forces, torques), then the dynamics are 
given by:
dx/dt=A(x)*u + b(x)
A(x) is a matrix that does not depend on u. My control algorithms need 
to be able to multiply a vector by the transpose of A(x).

In the simple 2D dynamics engine that I use, A(x) is obtained by 
inversing a matrix. In fact, the matrix is not inversed. It is simply 
LU-decomposed. I wonder if ODE has something similar, and how I could 
have access to it.

Thanks for helping me,

Rémi